Obstructive sleep apnea (OSA) is an important clinical disorder occurring in men, women, and children with a prevalence of 4%, 2% and 1-3%, respectively. OSA is under active study in adults and is definitely linked with increased cardiovascular morbidity, even in its mild to moderate clinical forms. In contrast, OSA has not been well studied in children and the potential deleterious consequences on cardiovascular function have received little or no attention. Our goal is to examine in children 1) The interaction between OSA and baroreflex dysfunction, 2) The relation of OSA severity and baroreflex dysfunction to abnormalities in blood pressure control during wakefulness and sleep, 3) The association of the diminished baroreflex gain and impaired blood pressure control with an index of end organ damage, the left ventricular mass index, and 4) Whether effective treatment of OSA results in significant improvement in baroreceptor function, blood pressure control and a decrease in left ventricular mass index. We will accomplish these aims by studying 8-12 year old children with OSA and a matched group of normal children in a cross-sectional design. We will study baroreceptor function, 24-hour ambulatory blood pressure and left ventricular mass index. Baroreceptor function will be measured by non-invasive techniques based on combined computer analysis of heart rate and blood pressure measured by portapres. 24-hour ambulatory blood pressure will be measured by a Spacelab monitor and left ventricular mass index will be measured by direct M-mode echocardiogram. In a longitudinal study we will study the effect of adequate treatment of OSA on baroreceptor function, daytime and nocturnal blood pressure and left ventricular mass index. We will follow a cohort of children with OSA and a matched group of normal controls for a period of 12 months after treatment of the disorder. Results are expected to show that children with OSA have decreased baroreceptor sensitivity, elevated nocturnal blood pressure and increased left ventricular mass index and that effective therapy for OSA, as determined by polysomnography, will improve or normalize baroreceptor sensitivity as well as nocturnal blood pressures and will lead to a decrease in left ventricular mass index. [unreadable] [unreadable]